To date, there is no published report of effects on marine mammal hearing
from underwater explosions. External injuries consistent with inner ear damage
have been found in dolphins subjected to Class C explosives, but often little
change is seen in surface animal behavior near blast areas [Richardson et al.,
OCS MMS/90-0093 (1991)]. In this study, temporal bones from two humpback
whales, which died following a 5000-kg explosion in Trinity Bay, Newfoundland
[Lien et al., J. Acoust. Soc. Am. 94, 1849(A) (1993)], were harvested,
preserved in formalin, scanned with 1-mm-high resolution spiral CT,
decalcified, and sectioned at 20 (mu). Evidence of mechanical trauma was found
in all four ears: Round window rupture, ossicular chain disruption,
sero-sanguinous effusion of peribullar spaces, and dissection of the middle ear
mucosa with pooled sera. In one animal, there were bilateral periotic
fractures. These observations are consistent with blast injury reports in
humans, particularly with damage to victims near the source who sustained
massive, precipitous increases in cerebrospinal fluid pressure. There was no
evidence that the pathologies found in these whales resulted from repeated
barotrauma or chronic infection, and no similar abnormalities were found in
control ears from humpbacks not exposed to blasts. While the results show
whales, like other mammals, are subject to severe blast trauma, it remains
unclear whether lower level stimuli induce temporary and/or acute threshold
shifts in marine mammals. [Work supported by ONR Grant. No. N00014-92-J-4000.]